This invention relates to a semiconductor device and a manufacturing method thereof, and is used particularly in a semiconductor device having high density wiring.
For forming wirings between internal portions of semiconductor elements or components and external portions and/or between or components elements and external portions in a semiconductor device, various materials are used. Especially, for metal wirings, an aluminum alloy, for example, of aluminum and silicon, an alloy of aluminum, silicon and copper, etc. are used.
Typically, an underlying structure of an electrode of polycrystalline silicon, etc. is formed on a semiconductor substrate and a wiring film made of an aluminum alloy is formed thereon. This wiring film is formed by depositing the aluminum alloy over the entire surface of the underlying structure using any one of such methods as sputtering, vacuum deposition and CVD, etc. to carry out patterning of a resist using photolithographic technique, and thereafter effecting etching with the resist as a mask.
For preventing the aluminum alloy. film from being exposed and corroded by moisture in the air, a protective inorganic insulating film is formed thereon. As this inorganic insulating film, phosphosilicate glass (PSG) is generally used.
Furthermore, multilevel wiring layer has often been formed in compliance with recent high density requirements. In such a multilayer structure, a first wiring film is formed on the underlying structure and a second wiring film is further formed thereon. In addition, an interlayer insulating film is deposited between these wiring films in order to ensure electrical insulating property therebetween. As this interlayer insulating film, silicon oxide film (SiO.sub.2) or silicon nitride film (Si.sub.3 N.sub.4) which has moisture-proof property and an excellent insulating property is ordinarily used. Such an insulating film may include an impurity such as phosphorus, and is used as a single film or a composite film. The wiring width or the line width tends to decrease each year in accordance with recent tendencies of high integration and high density and has been reduced to the order of micron or submicron in recent years. As a result, such problems as breakage of aluminum wiring of a product occur during test or use of a semiconductor device.
Such a breakage of aluminum wiring, is caused by thermal migration produced by thermal diffusion, electro migration produced by the movement of aluminum atoms as a result of a current flow, corrosion, and the like.
Where an interlayer insulating film is formed, using the chemical vapor deposition (CVD) method, as described above, it is required to raise temperature to 300.degree. to 450.degree. C. In such an elevated temperature condition, the deposited film is in an equilibrium state wherein the stress is small. However, when the temperature is lowered to room temperature, great stress will be accumulated in the aluminum film due to the difference between the coefficient of thermal expansion of aluminum and that of the deposited film. Namely, the stress created in the aluminum film containing 1% silicon immediately after the wiring is formed by etching of the film is 10.times.10.sup.8 dyn/cm.sup.2, whereas the stress created in the aluminum film after Si.sub.3 N.sub.4 film has been deposited by plasma CVD at a temperature of 300.degree. C. is changed to 30.times.10.sup.[ dyn/cm.sup.2. Thus it can be understood that the stress is considerably increased. Such a stress measurement is carried out by measuring the spacing between lattice planes by X-ray diffraction to compare the spacing measured with a lattice plane spacing when a known stress is created.
It has been known that when such a stress is created, the possibility of breaking the aluminum layer is greatly accelerated so that breakage is likely to occur.
Such problem also occurs in an interlayer insulating film of multilayer wiring. Particularly, breakage of the aluminum wiring which is the first layer presents the same problem. As a solution of this problem, a method has been proposed wherein a polyimide layer is formed between inorganic insulating films for the purpose of alleviating the stress of an aluminum wiring (e.g., Japanese Laid-Open patent specification No. 85724/1977). However, to form a polyimide layer, since it is required to dissolve the polyimide in a solvent to coat the solution and dry it, long-time heat treatments for drying and/or heat treatment for the subsequent polymerization are required. For this reason, the reduction of volume is large and it is difficult to form a flat polyimide layer on an irregular surface.
A further problem is that a polyimide layer has large water absorbing capability, resulting in a tendency to give rise corrosion of aluminum, and that polarization is produced as a result of application of a voltage for a long time and thus the threshold value of the transistor changes due to polarization, so that an erroneous operation is likely to occur.